Counter-current recirculating device for the exchange of heat between a gas and a finely granulated material



Jan. 14, '1958 J. ROSA El'AL 2,819,890

COUNTER-CURRENT RECIRCULATING DEVICE FOR THE EXCHANGE OF HEAT BETWEEN A GAS AND A FINELY GRANULATED MATERIAL Filed June 11, 1956 4 Sheets-Sheet 1 28%232/70/4 //3, 3?33 viig; 7 r

Jan. 14, 1958 J. ROSA ETAL 2,819,890 COUNTER-CURRENT RECIRCULATING DEVICE FOR THE EXCHANGE OF HEAT BETWEEN A GAS AND A FINELY GRANULATED MATERIAL Filed June 11, 1956 v 4 Sheets-Sheet 2 INVENTO 75m Yam, war/17m? Jr Jan. 14, 1958 J. ROSA EIAL 2,819,890

COUNTER-CURRENT RECIRCULATING DEVICE FOR THE EXCHANGE OF HEAT BETWEEN A GAS. AND A FINELY GRANULATED MATERIAL Filed June 11, 1956 4 Sheets-Sheet 3 65 Y 759 fi I J6 l fl 62 'i J6 l i 5/ l l 65 INVENTORS BY ip/4 Jan. 14, 1958 J. ROSA ETAL 2,819,890

COUNTER-CURRENT RECIRCULATING DEVICE FOR THE EXCHANGE OF HEAT BETWEEN A GAS AND A FINELY GRANULATED MATERIAL Filed June 11, 1956 v v 4 Sheets-Sheet 4 ay m z l United States "COUNTER-CURRENT RECIRCULATING DEVICE FOR THE EXCHANGE OF HEAT BETWEEN A GAS AND A FINELY GRANULATED MATERIAL Josef Rosa, Drasov, near Tisnov, and Vlastimil Petr, Brno, Czechoslovakia Application June 11, 1956, Serial No. 590,559

Claims priority, application Czechoslovakia June 14, 1955 5 Claims. (Cl. 263-21) a range of up to several hundreds centigrades in a mere fraction of a second, provided the particles of material are sufficiently small. In a similar way proceeds also a drying process and some other physical and chemical processes.

On the basis of this fact gases, sometimes also waste gases, are used for pre-heating, drying and the like operations carried out with various materials. A difiiculty arises, however, when in the course of the mixing operation the temperatures of the material and of the gas are at the utmost. equalised, so that either the final heating of the material with a small amount of gas is low, or when the amount of gas is larger, the degree of heating is higher, but in this case the gases leave with such a higher temperature.

According to some designs, for example, the pre-heating of fine grained materials is therefore carried out in such a way, that the material separated from the gas is .introduced into the stream of gas in front of the section in which the heating took place and the material is thus separated in stages from the gases and transferred against the direction of the stream of gases and comes therefore in contact with gases of always higher temperature. The devices in question consist of a series of cyclones placed above each other, the discharge portions of which are provided with various kinds of mechanical closures. Such devices have large dimensions and are relatively costly investments.

The present invention represents a considerable improvement in this respect.

The subject of the invention is a countercurrent recirculating device for the exchange of heat between a gas and a finely granulated material, said device'being intended for all cases of treatment of a finely granulated material by a stream of gas, when it is advantageous that such materialfor the purpose of increasing the effects of physical or chemical processes, taking place between the carrying gas and the treated material-should travel against the direction of the fiow of gas, such as is the case for instance in the course of a heating, drying, burning and'the like operations.

The invention is embodied by a device, in which the finely granulated material is entrained by a stream of gas in such a way, thatthe material is transferred in individual sections from a portion ofthe gas against the flow of gasin the heat exchange apparatus so that the material enters the device at the side of discharge of the carrying gas and leaves the device at the side of entry :of

2,819,896 Patented Jan. 14, 1958 the gas. This transfer of material against the direction of flow is achieved by a partial recirculation of the gas between the individual sections of the heat exchange apparatus, as will be disclosed hereinafter. Theoretically it would be possible with an infinite number of sections to achieve a heating of the material as high as the inlet temperature of the gases and cooling of the gases down to the inlet temperature of the material, which would mean a complete transfer of heat from the gas into the material. In practice, however, the number of sections is limited.

An example of the device according to the present invention is shown in the accompanying diagrammatic drawings, wherein:

Fig. 1 shows the diagram of operation of the exchange apparatus,

Fig. 2 shows an example of application of the device,

Fig. 3 shows another example,

Fig. 4 shows an example of mechanised burning of lime in powder form.

The principle of operation of the heat exchange apparatus is shown in Fig. 1. The exchange apparatus itself consists of a number of gas ducts for example 1, 2, 3, 4 and 5, as shown in the drawing. Thegas ducts are connected together by arcuate members 10, 1d, 18 and 22, so as to form a closed system. Gas enters the gas duct 1 through a tube 26 and leaves the gas duct 5 through a tube 33. At the end of each gas duct oblique sieves 12, 16, 2t], 24 and 28 are placed, said sieves consisting of fiat rails or rails profiled in a suitable way, arranged under an angle and overlapping each other when viewed in the direction of the flow of gas. The sieves are terminated in the direction of the flow of gas on the wall of the initial portion of the preceding gas duct. In these points slots 13, 17, 21 and 25 are provided in the partition walls of the gas duct, said slots connecting both neighbouring gas ducts. The preceding gas ducts into which open the sieves with. the slots are in these points suitably contracted in portions 11, 15, 19, 23 and 27. The material is supplied to the last duct 5 at its initial portion in the point 9 and leaves the heat exchange apparatus in the point 29 of the gas duct 1.

The described device operates as follows:

The carrying gas flows through the heat exchange apparatus in the direction ofv arrows with a velocity which is sufiicient for safely entraining the treated fine grained material. When the material is introduced in suitable batches into the stream of gas in the point 9, it is very finely dispersed and carried through the gas duct 5 in the direction .to the sieve 12. Here it strikes against the rails of the sieve and under theintluence of inertia proceeds in the. direction to the end portion (mouth) of the sieve in the .slot 13, while the carryinggas flows between the, rails into the discharge pipe 33. Due to the resistance caused by friction the staticpressure of the carrying gas in the gas duct 4 is, however, higher than that in the gas duct 5, so that the gas would have a tendency to flow through the slot 13 inthe direction 14-13-33.

In consequence of the contraction of the gas duct 4 in the point 15 and increase of velocity of the carrying gas and thus a change of the static pressure into dynamic pressure takes place in immediate vicinity of the slot. By a suitable choice of the contracted profile such a state may be reached that the static presssure in the gas duct 4 in the immediate vicinity of'the slot 13 will be lower than the static pressure in the gas duct 5. A portion of the gas from the mouth of the sieve 12 will therefore be sucked'through the slot 13 into the gas duct 4. This portion of'gas contains, however, also the material, which in thecourseof its passage overthe sieve has been compacted at the= mouth or discharge end of the sieve and conveyed together with the gas into the gas duct 4. A portion of gas from the gas duct 5 with the material contained therein comes in this way directly into the stream of gas, but in the gas duct 4, through which it is conveyed further in the direction of the arrow. On the sieve 16 of this gas duct the process is repeated, so that again a portion of gas with the material contained therein fiows through the slot 17 into the duct 3 etc., until it reaches the pipe 29 for the discharge of material.

The material has in this way actually passed through the entire exchange apparatus against the direction of flow of the carrying gas, without the necessity of stopping the material, separating it from the stream of gas or separating the individual stages of the exchange apparatus (gas ducts) from each other in any way whatsoever. The material may then easily be separated from this portion of gas for example by means of a cyclone separator 30, as shown in the enclosed drawing. The cleaned gas may be sucked from here in consequence of the difference in static pressures through a. pipe 32 connected to any of the preceding gas ducts or directly to the discharge pipe 33. The discharge portion of the said cyclone 3i) has to be provided with a pressure closure, e. g. automatic valves or flaps 31, a rotary closure (turning lock) or the like.

Examples of use The device disclosed above may be used for example in connection with burning of lime in pulverized condition.

The hitherto known method of burning lime in a shaft or annular furnace has considerable drawbacks. With a view to the method of burning the limestone has to be sorted, 40% of waste in the form of broken stones falling off in this operation, for which there is no suitable use and which considerably increase the cost of hauling the limestone. The sorting operation is a strenuous Work which in most cases has been performed by hand. The filling and discharging of annular furnaces, with which most of the lime kilns are equipped, is a particularly strenuous work, because it is carried out under great differences in temperature and cannot be mechanised in a suitable way. In connection with shaft furnaces the Work is partly mechanised, but the question of a suitable fuel has not yet been satisfactorily solved. When burning lime in a rotary furnace waste limestone splinters may be used but a great obstacle to the development and extension of this method is the substantially higher spe- ClfiC consumption of fuel as compared with the methods mentioned above. Moreover, the construction of rotary furnaces requires high investment costs.

All the above drawbacks are removed by the employment of the present invention for burning lime in pulverized condition.

Fig. 4 of the accompanying drawings shows an example of mechanised burning of lime in powder form.

The limestone hauled in a quarry, including splinters and possibly also with a small amount of admixtures is loaded by means of dredgers and conveyed into a crusher 70, from where it comes into a mill 71. The ground limestone proceeds through a pipe 72 into a storage tank 51, from where it is conveyed by a pneumatic conveying trough 52 with a fan 53 through a gravity tube 54 to the heat exchange apparatus 50.

The material is heated in the way disclosed above to the temperature of the admitted flue gases; it then proceeds heated and partly carbonised to a separator 56 provided with a double closure 57 and through a gravity tube 58 into a short rotary furnace 48, where the burning is completed. The burnt powder-like lime passes through a countercurrent cooler 73 where it is cooled by the countercurrent of air sucked in. From here the burnt powder-like lime is conveyed by a Fullers pump 74 through a pipe 75 to storage containers 76 from which dust is removed by means of a dust removing apparatus 4 77. The powder-like lime from the storage container may then either be filled in bags directly on a sack filling machine or may be hydrated to calcium hydrate and then filled in bags or artificial hydraulic lime may also be produced by an admixture of ground hydraulic ingredicuts.

The waste gases from the heat exchange apparatus 50 pass into a high efficiency separator 61, from where they are aspirated by a fan 65 through a pipe 64 and may be led either over a separator 78 into the atmosphere or through a pipe 79 to the grinding apparatus 71 for heating and drying of the material. The raw material retained in the separator 61 proceeds then over the pressure closure 62 through the gravity tubes 63 and 54 back into the heat exchange apparatus.

Further examples of use are shown in Figs. 2 and 3. In Fig. 2 a three-stage horizontal pressure heat exchange apparatus is shown, suggested as a drying plant for fine grain material. Carrying air is in this case sucked in by a fan 35 which drives the air over a heater 36 to the exchange apparatus 37. The powder-like material is supplied in batches from the storage tanks 38 to the exchange apparatus by a rotary closure 39. Dried material leaves the exchange apparatus through a tube 40 and is separated in a high efficiency cyclone 42. The exhaust 41 from the cyclone is attached to the second stage of the heat exchange apparatus. The air leaving the exchange apparatus through the tube 43 is filtered by a high efiiciency separator 44, from where it is lead into the atmosphere through an exhaust chimney 45.

Fig. 3 shows a five-stage vertical heat exchange apparatus arranged as a pre-heater of cement raw material for a rotary furnace. Flue gases from the rotary furnace 48 are aspirated through the exchange apparatus 50 by a fan 65. The raw material from the storage tank 51 is supplied to the exchange apparatus by means of a pneumatic conveying trough 52. The amount of raw material is controlled by a throttling valve 55. The raw material proceeds through the exchange apparatus in the way disclosed above and at the discharge portion of the apparatus it is received by a cyclone 56; through a pressure closure 57 and a gravity tube 58 it proceeds to the rotary furnace. The exhaust pipe 59 of the cyclone 56 is connected to the discharge pipe of the heat exchange apparatus 60. The exhausted gases are again filtered by the separator 61. The retained raw material may be fed over the pressure closure 62 and gravity tube 63 either back into the heat exchange apparatus or directly to the furnace, as shown in dotted lines in the drawing.

From the above examples it is obvious that the heat exchange apparatus may be carried out in numerous further modifications and variations and in connection with various devices not only as far as its arrangement itself and the provision of auxiliary equipment of the exchange apparatus are concerned, but also as to its use, without any change to the basic idea of the invention. It has therefore to be borne in mind that modifications carried out in this way fall within the scope of claims of this patent.

The use of the counter-current recirculating device brings considerable economical advantages. So for in stance when burning lime by means of the device disclosed above the costly sorting of material is dispensed with and the entire produced limestone, or even limestone partially soiled with clay, is utilized to the full. Furthermore any tiresome hand work is eliminated, because the entire process of production is fully mechanised. The result of the operation is lime in powder form, which the most required assortment both in agriculture and in the building industry, there being at the same time an easy possibility of production of artificial and natural hydraulic limes, and if desired even of hydration.

The burning of lime is exceedingly economicalwith regard to the fact that it is carried out in ground condition and that the heat of the flue gases is utilised to the asmeeo full. The investment costs due to the small dimensions and simplicity of the whole device are substantially lower than with the hitherto known methods of burning lime.

We claim:

1. A counter-current recirculating device for the exchange of heat between a gas and a finely granulated material for treating such material by a stream of gas, comprising in combination a predetermined number of gas ducts arranged next to each other, arcuate tubular members connecting the gas ducts in series, conduits for the gas and material to and from the gas ducts, the conduits for the material being provided for a fiow of the material counter-current to the general flow of gas, an oblique sieve consisting of rails mounted in each gas duct adjacent the end portion thereof, when viewed in the direction of the flow of gas, a slot in the wall of each gas duct provided in the vicinity of the farther end of the sieve, said farther sieve end being determined according to the direction of the flow of gas, each slot opening into the preceding gas duct, and means contracting the passage through each gas duct in the immediate vicinity of the slot so as to increase the velocity of the gas flowing therethrough, to transform static pressure into dynamic pressure, and to produce in the slot a pressure gradient of a reverse sense than in the remaining system, thus causing a flow of a portion of the gas with the material contained therein from the last gas duct through the respective slot to the preceding duct, and thence successively always through the respective slot from duct to duct in a direction counter-current to the general gas flow, the material being carried in the individual ducts co-current with the gas flow in each duct.

2. In the device according to claim 1, each of the slots opening from the far or downstream end of a duct, when viewed in the direction of the flow of gas, into the near or upstream end of the preceding duct.

3. In the device according to claim 1, said passagecontracting means being provided in the arcuate members.

4. In the device according to claim 1, said conduits including conduit means to withdraw said portion of gas mixed with the material, the device further comprising a dust separator to separate the portion of gas from the material, and a suction pipe connecting the dust separator with any one of the gas ducts.

5. In the device according to claim 1, said conduits including conduit means to Withdraw said portion of gas mixed with the material, the device further comprising a dust separator to separate the portion of gas from the material, and a suction pipe connecting the dust separator with the conduit discharging the general flow of gas.

Taylor Feb. 12, 1895 Meakin June 24, 1930 

